Marine and mobile rigs for drilling wells, such as oil and gas wells, are large and bulky. Transport of such rigs and stability are facilitated when the pipe hoisting equipment is incorporated in a mast which can be laid down horizontally to provide a low profile and low center of gravity.
The pipe racking equipment employed in fixed derricks as well as folding masts is also quite bulky and heavy, as well as costly, and adds to the instability and difficulties involved in laying down and raising a mast.